Wire bonding capillary vibration behaviour through Laser Doppler Vibrometry & its effects on wire bonding responses

Abstract

Ultrasonic vibration behavior of wire bonding capillaries was studied with laser vibrometer at free air and bonding stage. Vibration displacement was measured at transducer, capillary body and capillary tip at the interval of 1mm with Laser Doppler Vibrometer (LDV). This study focus on five different capillaries with same tip design, namely of three standard design capillaries with different main taper angle (MTA) and two special body cut capillaries. Wire bonding responses and capillary vibration behaviors was studied under different conditions. First, they were compared under same bond power setting. Second, each capillary were calibrated with same tip vibration displacement at free air by changing the bond power. Third same ball shear response was calibrated by adjusting bond power. In general, it is observed that when the vibration nodal position is farther from capillary tip (or higher), larger vibration displacement is generated at capillary tip. For special cut capillaries, capillary B with higher vibration nodal position than capillary A has shown larger tip vibration displacement, and it requires lesser bond power to produce same ball shear response. As for standard design capillary, with larger MTA, the vibration nodal position is lower and smaller tip vibration. Although with smaller tip vibration, it has shown better bonding results. The percentage of tip vibration displacement reduction for larger MTA capillary is lesser, and it requires lesser bond power to produce same ball shear response. From this study, we have understood that special cut capillary have different working principles than standard design capillary. The results of this study have demonstrated an in-depth understanding of the ultrasonic vibration behavior of different bonding capillary body design in both free air and bonding stage; and the impact on the wire bonding responses. Subsequently, this understanding is a step forward to develop the capillary material and design guideline.